Epilepsy surgery outcomes in temporal lobe epilepsy with a normal MRI.

TLDR: The objective is to determine the long‐term efficacy of anterior temporal lobectomy for medically refractory temporal lobe epilepsy in patients with nonlesional magnetic resonance imaging (MRI).

Abstract: Partial seizure disorders account for the majority of epilepsy (Sander et al., 1990). In one tertiary center cohort of 2,200 patients, partial epilepsy was more than twice as common as symptomatic, cryptogenic, and idiopathic generalized epilepsies combined. Moreover, in that study, two-thirds of the partial seizure disorders localized to the temporal lobe (Semah et al., 1998). Unfortunately, despite optimal medical therapy, approximately 30% of patients continue to experience recurrent seizures (Sander et al., 1990 Wiebe, et al. 2001). In a recent well-designed trial studying patients who failed initial medication trials, seizure freedom was achieved in only 8% of patients with continued medical therapy compared to 58% of patients undergoing anterior temporal lobectomy (Wiebe, et al. 2001). However, physicians may be reluctant to consider surgery for temporal lobe epilepsy when structural neuroimaging appears normal. Temporal lobectomy has been shown to render about 80% of patients seizure-free in the setting of a magnetic resonance imaging (MRI)–apparent structural abnormality concordant to the seizure onset zone, such as mesial temporal sclerosis (MTS) (Cascino, 2004). On the other hand, patients with temporal lobe epilepsy and normal MRI have received less attention. In order to demonstrate the absence of a potentially epileptogenic structural lesion, it is critical that patients have high-resolution seizure protocol MRI with both T1- and T2-weighted images (Jack, 1996; Cascino, 2004). There are relatively few studies examining temporal lobectomy in patients with normal modern seizure protocol MRI. Existing research suggests significantly disparate rates of successful surgery in patients with nonlesional MRI, ranging from 18–63% of patients becoming seizure-free (Berkovic et al., 1995; Theodore et al., 1997; Sylaja et al., 2004; Cohen-Gadol et al., 2005; Jeha et al., 2006). Many of these studies were conducted during the 1980s and early 1990s (Berkovic et al., 1995; Radhakrishnan et al., 1998; McIntosh et al., 2004), prior to the widespread use of epilepsy neuroimaging protocols that are more sensitive for detecting MTS (Jack, 1996; Jack et al., 1996). Some of these studies used pathologic findings to categorize patients (McIntosh et al., 2004; Cohen-Gadol et al., 2006), information that is not available preoperatively for clinical prognostication. Other studies include heterogeneous patient populations and only small numbers of patients with nonlesional MRI (Holmes et al., 2000; Sylaja et al., 2004; Cohen-Gadol et al., 2005). Therefore, we sought to examine the efficacy of epilepsy surgery and noninvasive predictors of favorable outcome for patients with medically refractory temporal lobe epilepsy and a nonlesional high-resolution seizure protocol MRI.